White Blood Cells: Infection Fighters

White Blood Cell (WBC) Count: WBCs (leukocytes) help prevent and fight infections in the body. The normal WBC count ranges 4,000-11,000 per cubic millimeter in an average healthy adult. A high WBC count may indicate your body is fighting an infection. Low counts may result from certain drugs (AZT or ganciclovir), minor viral infections, stress or opportunistic infections (tuberculosis, histoplasmosis, and other fungal infections). Low counts are a concern as the body becomes more susceptible to infection. White Cell Differential: This a breakdown of the different types of white blood cells as percentages of the total WBC count. The three main categories of white blood cells are: 1. lymphocytes, 2. granulocytes, and 3. monocytes.

Lymphocytes: Lymphocytes are white blood cells that produce antibodies and regulate the entire immune system. They make up 10-45% of your WBCs. There are two main categories: B-cells and T-cells, and they fight infection in different ways. CD4+ cells -- a type of T cell -- are cells that HIV targets. You may have heard the term "CD4+ count" or "T-cell count." (See Lymphocyte Subsets, for more information.)

Granulocytes (polymorphonuclear cells or PMNs): These are the most common types of WBCs, making up 55-80% of your total WBC count. PMNs are involved in fighting bacterial infections. Specific types of PMNs include:

Neutrophils
The most common type of white blood cell, they make up 55-70% of your WBC count. They fight infection in different ways, and play a key role in surrounding and destroying bacteria and other foreign substances in the body. Some drugs like ganciclovir (Cytovene) can decrease neutrophil counts.

Eosinophils
They make up 1-3% of WBC count and are involved in fighting parasitic infections and allergic reactions. Their numbers will rise during an allergic reaction or asthma attack.

Basophils
They make up only 1% of WBCs, but are very important for releasing histamine. Histamine is the substance that makes you feel congested and miserable during a cold (that is why we take anti-histamines to reduce cold symptoms), but they help your body heal by making the blood vessels "leakier" so the WBCs can travel faster to the areas of infection.

Monocytes: These make up 3-7% of WBCs. They circulate in the blood for about 24 hours and then move into tissues and mature into macrophages, which eat up infection and foreign bodies (macrophage means "big eater").